The simple derived shadow is of two kinds: one kind which has its
length defined, and two kinds which are undefined; and the defined
shadow is pyramidal. Of the two undefined, one is a column and the
other spreads out; and all three have rectilinear outlines. But the
converging, that is the pyramidal, shadow proceeds from a body that
is smaller than the light, and the columnar from a body equal in
size to the light, and the spreading shadow from a body larger than
the light; &c.